Sylvaemus dominans ( Kretzoi, 1962 )

Popov, Vasil V., 2004, Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (North Bulgaria), Geodiversitas 26 (3), pp. 403-491 : 456-460

Sylvaemus dominans ( Kretzoi, 1962) ( Figs 28 ; 29 )

Apodemus dominans Kretzoi, 1959: 243 (nomen nudum); 1962: 311, 357, pls IV, V. — De Bruijn et al. 1970: 544, 545, pl. I, figs 7-11. — Pasquier 1974: 42-44, pl. II, figs 4-7. — De Bruijn & Van der

Meulen 1975: 315-317, pl. 4, figs 1-8. — Van de Weerd 1979: 138-140, pl. 2, figs 1-9.

Apodemus occitanus Pasquier, 1974: 41 , 42, pl. 2.

Sylvaemus dominans – Dahlmann 2001: 79, 81.

MATERIAL EXAMINED. — 33 m 1 (Ms275-286), 12 m 2 (Ms287-293), 2 m 3 (Ms304-305), 34 M1 (Ms265- 274, 301-303), 19 M2 (Ms294-300).

MEASUREMENTS. — See Table 10.

DESCRIPTION

M1: this tooth is three rooted. Only one specimen possesses four roots. In some young specimens the t1 is shifted backward and is separated from the t2. Accessory small cusps t1 -bis and t2 -bis practically absent. Rarely, some specimens have a short backward directed spur on t3. The t4 is situated slightly anteriorly than the t6. The t4 and the t7 are disconnected. They fuse at latter stages of wear. The posterior cingulum (t12) is well developed.

M2: the number of roots is three (6 specimens) or four (2 specimens). Both t9 and t12 are well developed.

m1: the anterocentral cusp is well developed and sometimes isolated in unworn teeth, but it quickly connects to the posterior lamina with further wear. The anterior and the middle pairs of cusps are connected by a short sagittal ridge. The labial accessory tubercles are variable in size, shape and number. The posterior one, being the largest, is separated from the hypoconid in some specimens or fused with this tubercle in others. The other two or three add cusps are weak buds on a low cingular ridge. The terminal hell is of medium size.

m2: the anterolabial cusp is continuing posteriorly by a more or less complete labial ridge which may bear one or two small tubercles.

REMARKS

The overlap in dental morphology (size, occlusal pattern) in the two closely related recent species, Sylvaemus sylvaticus (Linnaeus, 1758) and S. flavicollis (Melchior, 1834) , is such that individual specimens are often indeterminable. As in recent forms, the determination of sympatric fossil species of the genus, based on dental features alone, meets with considerable difficulties.

According to the size, the available molars are larg- er than those of S. atavus Heller, 1936 from Gundersheim-4 ( Fejfar & Storch 1990). They belong to a medium sized form. Based on some primitive characters (M1 and M2 with three roots and a well developed posterior cingulum, a posterior shifting of the t1 on M1, etc.), one may distinguish the older medium sized forms, characteristic for the Pliocene and early Pleistocene, from the advanced forms of the Late Quaternary ( Pasquier 1974; De Bruijn & Van der Meulen 1975). According to Pasquier (1974), two European allopatric species occupied the lower evolutionary level – Sylvaemus occitanus ( Pasquier, 1974) (western Europe) and S. dominans ( Kretzoi, 1959) (Central and Eastern Europe). The differences between these forms are not impressive and concern the frequency of some details in the structure of the molars. It appears that the variation found between these species has the same range within species. According to De Bruijn & Van der Meulen (1975), the use of two specific names complicates the taxonomy unnecessarily. The available material confirms this point of view. The pattern of upper molars corresponds to Sylvaemus occitanus , while the lower ones are similar to S. dominans .

The presence of four roots in some M2s shows that the population from Muselievo is somewat more advanced, in comparison, for instance, with the form from Maritsa ( De Bruijn et al. 1970). The larger size of the molars from Muselievo in comparison with these of S. dominans from the early Ruscinian in Greece ( Van de Weerd 1979) should also be interpreted in this direction.

Family CRICETIDAE Murray, 1866

Figures

FIG. 28. — Sylvaemus dominans (Kretzoi, 1962), upper molars in occlusal view; A, right M1, Ms265; B, right M1, Ms266; C, right M1, Ms267; D, right M1, Ms268; E, right M1, Ms269; F, right M1, Ms272; G, left M2, Ms297; H, right M2, Ms298; I, right M2, Ms294. Scale bar: 1 mm.

FIG. 29. — Sylvaemus dominans (Kretzoi, 1962), lower molars in occlusal view; A, right m1, Ms269; B, right m1, Ms284; C, right m1, Ms277; D, left m1, Ms281; E, left m1, Ms279; F, right m1, Ms278; G, right m1, Ms276; H, right m1, Ms280; I, left m2, Ms292; J, right m2, Ms287; K, left m2, Ms288; L, right m2, Ms290. Scale bar: 1 mm.